1,389 research outputs found
Neutralino Annihilation into a Photon and a Z boson
A full one-loop calculation of neutralino S-wave annihilation into the
final state is performed in the minimal supersymmetric extension of
the Standard Model. This process, like the similar one with two photons in the
final state, may be of importance for the indirect detection of supersymmetric
dark matter through the very narrow ray line that would result from
neutralino annihilations in the galactic halo.
We give the complete analytical formulas for this loop-induced process and
treat the case of a pure Higgsino as a first application of our expressions.
Predictions for the gamma line flux are given for the halo model which is of
the form suggested by Kravtsov et al. and for the profile proposed by Navarro,
Frenk and White.
For heavy neutralinos, the lines from and would have
indistiguishable energy in a realistic detector, making the fluxes add and
facilitating discovery. For lighter neutralinos, the positions and relative
strengths of the two lines would give valuable information on the nature of the
supersymmetric dark matter particles.Comment: 19 pages, LaTeX, 6 eps figures. Some formulas corrected, improved
discussion of halo models, results and conclusions unchanged. Version to
appear in Phys. Rev.
Two photon annihilation of Kaluza-Klein dark matter
We investigate the fermionic one-loop cross section for the two photon
annihilation of Kaluza-Klein (KK) dark matter particles in a model of universal
extra dimensions (UED). This process gives a nearly mono-energetic gamma-ray
line with energy equal to the KK dark matter particle mass. We find that the
cross section is large enough that if a continuum signature is detected, the
energy distribution of gamma-rays should end at the particle mass with a peak
that is visible for an energy resolution of the detector at the percent level.
This would give an unmistakable signature of a dark matter origin of the
gamma-rays, and a unique determination of the dark matter particle mass, which
in the case studied should be around 800 GeV. Unlike the situation for
supersymmetric models where the two-gamma peak may or may not be visible
depending on parameters, this feature seems to be quite robust in UED models,
and should be similar in other models where annihilation into fermions is not
helicity suppressed. The observability of the signal still depends on largely
unknown astrophysical parameters related to the structure of the dark matter
halo. If the dark matter near the galactic center is adiabatically contracted
by the central star cluster, or if the dark matter halo has substructure
surviving tidal effects, prospects for detection look promising.Comment: 17 pages, 3 figures; slightly revised versio
Evolving rules for document classification
We describe a novel method for using Genetic Programming to create compact classification rules based on combinations of N-Grams (character strings). Genetic programs acquire fitness by producing rules that are effective classifiers in terms of precision and recall when evaluated against a set of training documents. We describe a set of functions and terminals and provide results from a classification task using the Reuters 21578 dataset. We also suggest that because the induced rules are meaningful to a human analyst they may have a number of other uses beyond classification and provide a basis for text mining applications
Running mass of the rho0 meson's implication for the dilepton mass spectrum and the mu+mu-/e+e- branching ratio in the K+ --> pi+l+l- decays
We make an attempt to resolve the discrepancy of the observed e+e- mass
spectrum in the K+ --> pi+e+e- decay with that predicted by meson dominance. To
this end we investigate the properties of the rho0 propagator. We use
dispersion relations to evaluate the running mass squared m_rho^2(t) of the
rho0 resonance without adjustable parameters. To improve the convergence of the
dispersion integral, the momentum dependence of strong vertices is taken from
the flux-tube-breaking model of Kokoski and Isgur. The obtained behavior of
m_rho^2(t) at small momentum squared t makes the K+ --> pi+e+e- form factor
rise faster with increasing than in the original meson-dominance
calculation and more in agreement with the published data. As a consequence,
the meson-dominance prediction of the mu+mu-/e+e- branching ratio changes
slightly, from 0.224 to 0.236. We do not see any possibility to accommodate
into the meson-dominance approach an even steeper e+e- spectrum, indicated by
the preliminary data of the E865 collaboration at BNL AGS.Comment: 13 pages, RevTeX, epsf.sty, 4 embedded figure
Diffuse inverse Compton and synchrotron emission from dark matter annihilations in galactic satellites
Annihilating dark matter particles produce roughly as much power in electrons
and positrons as in gamma ray photons. The charged particles lose essentially
all of their energy to inverse Compton and synchrotron processes in the
galactic environment. We discuss the diffuse signature of dark matter
annihilations in satellites of the Milky Way (which may be optically dark with
few or no stars), providing a tail of emission trailing the satellite in its
orbit. Inverse Compton processes provide X-rays and gamma rays, and synchrotron
emission at radio wavelengths might be seen. We discuss the possibility of
detecting these signals with current and future observations, in particular
EGRET and GLAST for the gamma rays.Comment: 13 pages, 5 figure
Non-Baryonic Dark Matter - Observational Evidence and Detection Methods
The evidence for the existence of dark matter in the universe is reviewed. A
general picture emerges, where both baryonic and non-baryonic dark matter is
needed to explain current observations. In particular, a wealth of
observational information points to the existence of a non-baryonic component,
contributing between around 20 and 40 percent of the critical mass density
needed to make the universe geometrically flat on large scales. In addition, an
even larger contribution from vacuum energy (or cosmological constant) is
indicated by recent observations. To the theoretically favoured particle
candidates for non-baryonic dark matter belong axions, supersymmetric
particles, and of less importance, massive neutrinos. The theoretical
foundation and experimental situation for each of these is reviewed. Direct and
indirect methods for detection of supersymmetric dark matter are described in
some detail. Present experiments are just reaching the required sensitivity to
discover or rule out some of these candidates, and major improvements are
planned over the coming years.Comment: Submitted to Reports on Progress in Physics, 59 pages, LaTeX, iopart
macro, 14 embedded postscript figure
On Dark Matter Annihilation in the Local Group
Under the hypothesis of a Dark Matter composed by supersymmetric particles
like neutralinos, we investigate the possibility that their annihilation in the
haloes of nearby galaxies could produce detectable fluxes of -photons.
Expected fluxes depend on several, poorly known quantities such as the density
profiles of Dark Matter haloes, the existence and prominence of central density
cusps and the presence of a population of sub-haloes. We find that, for all
reasonable choices of Dark Matter halo models, the intensity of the
-ray flux from some of the nearest extragalactic objects, like M31, is
comparable or higher than the diffuse Galactic foreground. We show that next
generation ground-based experiments could have the sensitivity to reveal such
fluxes which could help us unveiling the nature of Dark Matter particles.Comment: 11 pages, 10 figures. Accepted for publication in Phys. Rev. D.;
added a new paragraph on the detectability of Galactic sub-halos in our
Galaxy; added a discussion on their model dependence. The relation of our
results with the "CDM crisis" issue has also been adde
Suppressing Unwanted Memories Reduces Their Unintended Influences
The ability to control unwanted memories is critical for maintaining cognitive function and mental health. Prior research has shown that suppressing the retrieval of unwanted memories impairs their retention, as measured on intentional (direct) memory tests. Here we review emerging evidence revealing that retrieval suppression can also reduce the unintended influence of suppressed traces. In particular, retrieval suppression (1) gradually diminishes the tendency for memories to intrude into awareness, and (2) reduces memories’ unintended expressions on indirect memory tests. We present a neural account in which, during suppression, retrieval cues elicit hippocampally-triggered neocortical activity that briefly reinstates features of the original event, which, in turn, are suppressed by targeted neocortical and hippocampal inhibition. This reactivation-dependent reinstatement principle could provide a broad mechanism by which suppressing retrieval of intrusive memories limits their indirect influences
Indirect signals from light neutralinos in supersymmetric models without gaugino mass unification
We examine indirect signals produced by neutralino self-annihilations, in the
galactic halo or inside celestial bodies, in the frame of an effective MSSM
model without gaugino-mass unification at a grand unification scale. We compare
our theoretical predictions with current experimental data of gamma-rays and
antiprotons in space and of upgoing muons at neutrino telescopes. Results are
presented for a wide range of the neutralino mass, though our discussions are
focused on light neutralinos. We find that only the antiproton signal is
potentially able to set constraints on very low-mass neutralinos, below 20 GeV.
The gamma-ray signal, both from the galactic center and from high galactic
latitudes, requires significantly steep profiles or substantial clumpiness in
order to reach detectable levels. The up-going muon signal is largely below
experimental sensitivities for the neutrino flux coming from the Sun; for the
flux from the Earth an improvement of about one order of magnitude in
experimental sensitivities (with a low energy threshold) can make accessible
neutralino masses close to O, Si and Mg nuclei masses, for which resonant
capture is operative.Comment: 17 pages, 1 tables and 5 figures, typeset with ReVTeX4. The paper may
also be found at http://www.to.infn.it/~fornengo/papers/indirect04.ps.gz or
through http://www.astroparticle.to.infn.it/. Limit from BR(Bs--> mu+ mu-)
adde
D-wave heavy quarkonium production in fixed target experiments
We calculate the -wave heavy quarkonium production at fixed target
experiments under the NRQCD factorization formalism. We find that the color
octet contributions are two orders of magnitude larger than color-singlet
contributions if color-octet matrix elements are taken according to the NRQCD
velocity scaling rules. Within the theoretical uncertainties, the prediction
for the production rate of -wave charmonium state agrees with the
preliminary result of E705 and other experiments. Searching for the
-wave state is further suggested.Comment: 13pages, 4 PS figures, final vertion to appear in PR
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